Move header fields into TOP level of Parcels.

Details:
* Parcels were originally 2 element hashes: headers and message.
  But now, we're promoting the header elements to the top level
  and reserving a bunch of property names for Serf's use.
* Promotes 'kind' to the top level property of a parcel.
* Promotes UUIDs (uuid, parent_uuid and origin_uuid) to be top level
  properties of a parcel.
* Serf Reserves the following field names in the top level parcel:
  kind, uuid, parent_uuid, origin_uuid, message and the serf_* names.
* Other unreserved header names SHOULD be namespaced by app/module.
* Renames RequestTimer header to 'serf_elapsed_time'.
  Also fixes access to serf_elapsed_time field by using the '[]' method
  to conform with idea that the parcel may just be a plain Hash, not
  Hashie::Mash.
* Most of the real change revolves around the ParcelFactory.
  All other stuff was fixups to match the parcel change.
* Updates the specs to look for headers in the top level of the parcel.
  Mostly for the 'kind' field.
* FIX: UuidTagger middleware now adds the UUID to a dup'd parcel instead of
  modifying the given input parcel.
* Random fixups of incorrect comments. (eg. Middleware class comments)
* Reduce/Generalize the FactoryGirl object creation.
* Updated README and examples and specs to reflect these changes.
Update copyright NOTICE w/ new year 2013.